The present invention relates to an once through fan for circulating a laser gas of an excimer laser apparatus, and more particularly to an once through fan for an excimer laser apparatus having a small vibration and being capable of rotating at a high rotational speed.
Conventionally, an once through fan in which a rotary shaft is supported by a magnetic bearing has been known as an once through fan for circulating a laser gas of an excimer laser apparatus.
FIGS. 5 and 6 show an embodiment which the applicant of this patent application disclosed in Japanese Patent Unexamined Publication No. 10-173259. FIG. 5 is a side elevational cross sectional view which shows a total structure of an excimer laser apparatus and FIG. 6 is a detailed view of a P portion in FIG. 5. Hereinafter, a prior art will be described on the basis of these drawings.
A laser gas corresponding to a medium for oscillating a laser beam is sealed within a chamber 2 of the excimer laser apparatus. An once through fan 1 provided with a rotary shaft 4 and a blade portion 6 having a plurality of blades is arranged at a predetermined position of the chamber 2, and it is structured such as to circulate a laser gas so as to introduce between discharge electrodes 3 and 3 by applying a driving force to the rotary shaft 4 so as to rotate the blade portion 6. The excimer laser apparatus applies a predetermined high voltage between the discharge electrodes 3 and 3, thereby exciting a laser gas and oscillating a laser beam.
The once through fan 1 is structured such that the rotary shaft 4 thereof is rotatably supported by non-contact magnetic bearings 7 and 7. The magnetic bearings 7 and 7 are provided with permanent magnets 10 and 10 which are annually mounted on an outer periphery of the rotary shaft 4 and integrally rotating with the rotary shaft 4 and permanent magnets 11 and 11 which annually surround an outer periphery of the permanent magnets 10 and 10 at a predetermined interval. Then, an opposing surface between the permanent magnet 10 and the permanent magnet 11 is set to the same pole, and the rotary shaft 4 is rotatably supported in a non-contact state by utilizing a repulsion force between the permanent magnets 10, 10, 11 and 11.
Further, a permanent magnet 13 is mounted to an end (a right end in the drawing) of the rotary shaft 4 in the once through fan 1, and the permanent magnet 13 is opposed to a permanent magnet 14 via a barrier portion 12. The permanent magnet 14 is mounted to a motor rotary shaft 17 of a motor 15 mounted to an outer wall of the chamber 2, and the permanent magnets 13 and 14 and the barrier portion 12 constitute a magnetic torque coupling 16 for transmitting a drive force of the motor 15 to the once through fan 1.
However, in the excimer laser apparatus, since a pressure of a laser gas is high (normally 2 atmospheric pressure or more), a resistance of the laser gas is great when the once through fan 1 rotates therewithin, so that the once through fan 1 terribly vibrates. This vibration is transmitted to the chamber 2 and an optical axis of an optical part (not shown) in the excimer laser apparatus is shifted, so that there is a case that a characteristic of the laser beam is deteriorated.
Further, since the rotary shaft 4 of the once through fan 1 and the motor rotary shaft 17 are separated, it is hard to completely coincide center axes for rotation of the both, so that there is a case that the center of the rotation is shifted. Accordingly, an ununiform force is applied to the rotary shaft 4 and the once through fan 1 is vibrated, however, means for restricting the vibration of the once through fan 1 is not disclosed in the publication mentioned above.
Further, in recent years, there is a requirement of increasing an oscillating frequency of the laser beam so as to improve a capacity for processing in the case of performing a light beam process such as a lithography or the like by using an excimer laser apparatus as a light source. In order to increase the oscillating frequency of the laser beam, it is necessary to increase the rotational speed of the once through fan 1 so as to increase a flow amount of the circulating laser gas, however, in the case of the conventional once through fan 1, the vibration is terribly generated and the rotational speed can not be increased.
Further, in the prior art, the rotation of the motor 15 is transmitted to the once through fan 1 via the magnetic torque coupling 16. At this time, when increasing the rotation of the motor 15, a load for rotating the once through fan 1 is increased, so that there is a case that the permanent magnet 13 slips with respect to the rotation of the permanent magnet 14 and can not follow the rotation of the permanent magnet 14. Accordingly, the torque of the motor 15 is not transmitted to the once through fan 1 and the rotational speed of the once through fan 1 can not be increased.
The present invention is made by taking the problems mentioned above into consideration, and an object of the present invention is to provide an once through fan for an excimer laser apparatus in which a vibration is reduced and a rotational speed can be increased.
In order to achieve the object mentioned above, in accordance with a first aspect of the present invention, there is provided an once through fan for an excimer laser apparatus, comprising a blade portion having a plurality of blades, a rotary shaft for rotating the blade portion and a magnetic bearing rotatably supporting the rotary shaft in a non-contact manner so as to circulate a laser gas sealed within a chamber in accordance with a rotation of the blade portion, wherein a rotor of a motor installed within the chamber and rotating the rotary shaft is mounted on an outer peripheral portion of the rotary shaft.
In accordance with the first embodiment, the rotor is mounted to the rotary shaft of the once through fan and a stator is arranged in such a manner as to surround the outer peripheral portion thereof, whereby the rotor and the stator constitute the motor. As mentioned above, since the rotary shaft of the motor corresponding to the drive source and the rotary shaft of the once through fan are made the same, the center axes of the rotation of the both coincide with each other, and it is possible to drive the rotary shaft by a uniform force. Further, in comparison with the case that the connecting portion or the like is provided in the middle of the rotary shaft, it is possible to adjust a rotational balance of the rotary shaft in a significantly accurate manner.
Accordingly, since the vibration of the once through fan is reduced, the optical axis of the optical element of the excimer laser apparatus is hardly shifted, and the characteristic of the laser beam is stabilized.
Further, since the motor rotary shaft and the rotary shaft of the once through fan are made the same, the drive force is transmitted with no loss. Further, since there is no connection portion in the middle of the rotary shaft, a strength of the rotary shaft is increased, so that the rotary shaft is not twisted even when increasing the rotational speed.
Accordingly, since it is possible to rotate the once through fan at a higher rotational speed, it is possible to increase a circulating flow amount of the laser gas so as to increase the oscillating frequency of the laser beam.
In accordance with a second aspect of the present invention, there is provided an once through fan as recited in the first aspect, wherein at least one magnetic bearing for supporting the rotary shaft is arranged in an outer side in an axial direction of the rotor.
In accordance with the second aspect, the magnetic bearing is arranged in the outer side of the rotor. Accordingly, since the rotor having a heavy weight is arranged in an inner side of the magnetic bearing supporting the rotary shaft, it is possible to support the weight of the rotor in a more stable manner, so that the vibration of the once through fan is reduced.
In accordance with a third aspect of the present invention, there is provided an once through fan as recited in the first aspect, wherein at least one magnetic bearing for supporting the rotary shaft is arranged in each of both sides in an axial direction of the rotor.
In accordance with the third aspect, the magnetic bearings are arranged in both sides of the rotor. Accordingly, since the rotors corresponding to the drive source and having a heavy weight are arranged in the inner sides of two magnetic bearings, the rotor can be supported in a more stable manner and the vibration thereof can be reduced.
In accordance with a fourth aspect of the present invention, there is provided an once through fan as recited in the third aspect, wherein a magnetic force of the magnetic bearing arranged between the rotor and the blade portion is set to be greater than a magnetic force of the magnetic bearing arranged in a portion except the portion therebetween.
In accordance with the fourth aspect, the magnetic bearing having the magnetic force stronger than that of the other magnetic bearings is arranged between the rotor and the blade portion. That is, since the magnetic bearing having the strongest magnetic force is arranged near the center portion of the rotary shaft which has the greatest amplitude of the vibration of the rotary shaft and to which the weight heavier than the other magnetic bearings is applied, it is possible to effectively restrict the vibration of the rotary shaft.
In accordance with a fifth aspect of the present invention, there is provided an once through fan as recited in the third aspect, wherein a length in a direction of the rotary shaft of the magnetic bearing arranged between the rotor and the blade portion is set to be longer than a length in a direction of the rotary shaft of the magnetic bearing arranged in a portion except the portion therebetween.
In accordance with the structure of the fifth aspect, since it is possible to restrict the vibration near the center portion of the rotary shaft in a wide range, it is possible to restrict the vibration of the rotary shaft in a more effective manner.